Change VariadicOperatorMatcherInterface<> to take an ArrayRef<DynTypedMatcher>.

Summary:
Change VariadicOperatorMatcherInterface<> to take an ArrayRef<DynTypedMatcher>.
This simplifies its implementation and use.
Also reduces the number of symbols in Registry.cpp.o, which we are always in need.

Reviewers: klimek

CC: cfe-commits, revane, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D2216